1. Technical Field
The present invention relates to medium transport apparatuses provided with curved transport paths that transport a medium while bending that medium, and to scanner apparatuses and recording apparatuses provided with such medium transport apparatuses.
2. Related Art
An ink jet printer serves as an example of a recording apparatus or a liquid ejecting apparatus. In recent years, what are known as complex machines, in which an ink jet printer is provided both with printer functionality and scanner functionality, have become mainstream. A complex machine is capable of reading a document and recording onto paper using a single machine, and is thus not only convenient, but also saves space.
There are cases where the scanner is provided with an auto document feeder (ADF) for the document, and is configured so as to be capable of automatically feeding and reading a plurality of documents. As a configuration for such an auto document feeder, JP-A-2010-28546 employs a configuration in which a document is fed out from a document tray, is inverted in a U-shape by a roller, and is transported to a reading position, after which the document is discharged toward a discharge tray.
Note that the configuration for inverting the sheet in a U-shape and transporting the sheet is not limited to auto document feeders provided in scanners, and is also used in paper transport paths of ink jet printers, as disclosed in JP-A-2002-68494 and JP-A-8-157107.
Incidentally, with an auto document feeder provided in a scanner, a paper transport apparatus in a printer, or the like, skew (inclination) in the paper has thus far been eliminated using paper feed control. For example, JP-A-2002-68494 discloses a skew removal method that uses the so-called “nip-and-release” technique. This skew removal technique carries out control so that a sheet is first nipped by a transport roller pair, and after the leading edge of the sheet has been fed downstream by the transport roller pair by a predetermined amount, and the rotation of the transport roller pair is reversed, thus releasing the leading edge of the sheet upstream from the transport roller pair. At this time, the sheet that has been released upstream from the transport roller pair flexes on the upstream side of the transport roller pair, and thus the leading edge of the sheet follows the transport roller pair; this removes the skew of the sheet.
Accordingly, it is desirable, from the standpoint of removing the skew with certainty, for the space where the sheet flexes upstream from the transport roller pair to be large; however, when not carrying out skew removal, a large space in the paper transport path makes it easier for path deviation to occur to the left and right, and is thus not desirable. In light of this situation, in JP-A-2002-68494, a mobile member that serves as an assisting member is provided in a curved inverting path. This assisting member (mobile member) is provided on the outer side of the curved inverting path, and is normally in a position that narrows the space of the paper transport path; however, when removing skew, the assisting member is pressed upon by the sheet and thus retracts to the outer side of the curved inverting path, thus securing a space in which the sheet can flex to a sufficient degree.
However, there are flimsy types of paper and rigid types of paper, and thus if the biasing force of a biasing unit that biases the assisting member is set for, for example, a flimsy type of paper, and a rigid type of paper is then transported, the assisting member will retract not only during skew removal but also during normal paper transport, and thus the original goal of the assisting member cannot be achieved. Conversely, if the biasing force of the biasing unit that biases the assisting member is set for a rigid type of paper, the assisting member cannot retract when carrying out skew removal for a flimsy type of paper, and thus the original goal of the assisting member once again cannot be achieved. In other words, it is difficult to set an appropriate load for the assisting member, and there has thus been a problem in that the level of allowance for that load is low. This type of technical problem is not considered by the past techniques disclosed in JP-A-2010-28546, JP-A-2002-68494, and JP-A-8-157107.